The present invention relates generally to self-closing valve mechanisms.
Having reference to the prior art patents noted above, it will be seen that it has been generally known to provide self-closing valve arrangements of the type which utilize a dashpot arrangement for controlling the closing time of the valve. Commonly, such arrangements comprise a piston member connected with the main valve, the piston member being reciprocably movable within a timing chamber, and means being provided for controlling biased movement of the valve into a seated closed position.
The known prior art structures differ primarily in the structural arrangement of the piston timing means and the manner of adjusting the timing interval. A major consideration in self-closing valves utilizing a dashpot timing arrangement, is to utilize a structure such that the valve will require little maintenance, and once the timing interval is adjusted it will maintain the timing interval with a minimum variation for relatively long periods of operation, and require little or no resetting or adjustments.
The present invention is considered to constitute an improvement particularly with respect to self-closing valve structures such as disclosed in the above-noted prior art U.S. Pat. Nos. 1,995,792 and 3,038,169. In each of these patents, the valve closing time interval is determined by a dashpot arrangement in which the spring biased piston is moved in a closing direction at a rate determined by fluid flow into the timing chamber through a bleeder opening at a rate controlled by a screw compressible porous material in the form of a felt washer. With such arrangements, it has been found difficult to maintain a constancy of the timing interval over relatively long periods of time; and in order to adjust the timing interval by changing the compressing screw for the felt washer, it is necessary to disassemble the valve and exercise procedures which are time consuming and difficult to effect.
In the present invention, the self-closing valve mechanism has in general been redesigned throughout in order to provide improved operating characteristics which will require little attention and which will be maintained over relatively long periods of operation.
In this respect, an important feature is that, instead of utilizing a compressible felt washer or other variable means for controlling the bleeder opening, the inlet fluid flow through the bleeder opening is controlled by a fixed hydraulic restriction in the form of a capillary tube coiled around the exterior of the dashpot. This capillary tube is nominally 0.013 inch inside diameter and approximately 1.5 feet in length. The outlet end of this tube forms the bleed opening, and the inlet end of the tube is fitted with an uncompressed porous plastic filter to protect the tube from clogging.
Another feature of the present invention resides in the provision of readily accessible means for adjusting the closing stroke of the valve. For this purpose, the outer end of the valve stem is provided with an axially adjustable cap formed with an abutment stop, this cap being adjustable to vary the open position of the valve, as determined by the stop, and consequently the interval of time required to close the valve.
Another feature of the present invention comprises the use of a relatively much longer coiled spring for biasing the valve in a closing direction. This spring has a lower spring rate which provides a more even biasing force during timing and a higher final closure force in the closed position of the valve.
As a result of the above-mentioned features, tests of valve structures incorporating these features have indicated that the timing has been held within a 2 second total tolerance for more than 27,000 cycles without cleaning or other servicing, and that some of the valve components have been operated well over 75,000 cycles.